This invention relates to a method of treating pentachlorophenol to reduce its tendency to bloom or sublime and to the treated pentachlorophenol thereby obtained.
Pentachlorophenol is a well known fungicide and preservative which is widely used to preserve wood, particularly that which is exposed to the soil or other sources of moisture. Pentachlorophenol is sold in bulk as a granular solid, either flakes or prills. The solid material, particularly when freshly prepared, has a strong tendency to bloom or sublime whereby very fine crystals form on the surface. This coating of crystals is easily dislodged during handling and opening a container can release a cloud of dust which is intensely irritating to eyes, nose, and throat.
Pentachlorophenol has been treated in a number of ways to avoid this problem. The granular material has been tumbled in hot air to make a product having a smooth surface and less tendency to bloom (Canadian Pat. No. 749,423). It has been treated with diethanolamine or triethanolamine to reduce dusting and residual acid (U.S. Pat. No. 3,646,225). Oil treatments have long been used for dusty solids and pentachlorophenol has been given a dual treatment with oil and a glycol to reduce dusting (U.S. Pat. No. 3,692,561). All of these treatments are effective to some degree, but most have economic or other disadvantages. The effect of some is of short duration and blooming may start a few days or weeks after the treatment. Hot air treatment may increase the formation of insoluble sludges upon dissolving the treated pentachlorophenol in a solvent to treat wood. Oil tends to darken the treated pentachlorophenol and it may cause staining or deterioration of the container.